Rainbow refractometry has been investigated numerically for small droplets under ultrashort pulse illumination. Using Fourier Lorenz-Mie Theory, local maxima of the scattering function were investigated as a function of the scattering angle, particle size and refractive index. The primary rainbow was shown to be detectable for pulse lengths as short as 1.0 fs and free of interferences with other scattering orders for droplet diameters down to 5 mu m. An extension of the Generalized Lorenz-Mie Theory was used to obtain an estimation of the influence of nonsphericity on refractive index detection. Overall, the possibility of improved in situ temperature measurements with Rainbow refractometry for small particles was shown to be feasible.